Compression Apparatus

ABSTRACT

Provided is a compression apparatus that can appropriately cool a motor even in a high-temperature operation environment. A rotating shaft, a main compressor attached to the rotating shaft, and which compresses ambient gases and to emit a compressed gas, a motor attached to an upstream side of the main compressor on the rotating shaft, and which drives the main compressor, a turbine provided at the upstream side of the main compressor, and which expands a part of the ambient gas to generate a low-temperature gas to be used to cool the motor, and a sub compressor provided at the upstream side of the main compressor and at a downstream side of the turbine, and which compresses the low-temperature gas used to cool the motor to pressure equal to the ambient gas, wherein the main compressor generates the compressed gas by mixing and compressing the low-temperature gas compressed by the sub compressor and a part of the remaining ambient gas.

TECHNICAL FIELD

The present invention relates to a compression apparatus, and especiallyrelates to a compression apparatus used in a high-temperatureenvironment.

BACKGROUND ART

In natural gas fields, gas wells that reach a gas layer from the groundare developed, and a natural gas accumulated in the gas layer is causedto flow in an artesian manner and is collected. In the beginning of thedevelopment of the gas wells, the pressure of the gas layer is high, andthe natural gas can be caused to flow to the ground in an artesianmanner. However, as the natural gas is continuously collected, thepressure of the gas layer is decreased, and the artesian flow stops whenthe pressure falls below a certain limit pressure. Therefore,conventionally, the gas field, in which the pressure of the gas layerfalls below the limit pressure, is regarded to be exhausted even if asubstantial amount of natural gas still remains in the gas layer.

However, methods of collecting the natural gas from the gas field wherethe artesian flow stops have been discussed on the background of anincrease in energy price and development of mining technologies. As oneof the methods, a method of installing a compression apparatus on abottom portion of a gas well, and increasing the pressure of the naturalgas in the gas layer and sending the natural gas to the ground has beensuggested, and research and development of the compression apparatus(downhole compression apparatus) for implementing the method iscurrently underway.

Since the bottom portion of the gas well has a severe environmentalcondition, the downhole compression apparatus is required to have highenvironment-resistant performance. Especially, since a motor used forthe downhole compression apparatus has a relatively low heat-resistanttemperature, a technology to appropriately cool the motor is essentialto realize the downhole compression apparatus, which is operated on thebottom portion of the gas well with a high environmental temperature.Compression apparatuses including means for cooling a motor aredescribed in PTL 1 and PTL 2, for example.

PTL 1 discloses, regarding a compression apparatus used in a gas well, aconfiguration to cool a compressed gas by heat exchange with an outside,and brings a part of the cooled compressed gas in contact with a motor,thereby to cool the motor. Meanwhile, PTL 2 discloses, regarding acompression apparatus for underwater operation, a configuration to coola motor, using a coolant circulating inside and outside the compressionapparatus.

CITATION LIST Patent Literatures

PTL 1: JP 2012-013072 A

PTL 2: JP 2009-530537 W

SUMMARY OF INVENTION Technical Problem

Both of the systems of cooling a motor disclosed in PTL and PTL 2 useheat exchange with an outside, and can appropriately decrease thetemperature of the motor if the systems are applied to a compressionapparatus operated on a ground with a low environmental temperature orunderwater.

However, for example, in a case of a downhole compression apparatus thatis operated deep in the ground, the environmental temperature is high,and the cooling system that uses heat exchange with an outside may notbe able to appropriately cool the motor.

The present invention has been made in view of the above problems, andan objective is to provide a compression apparatus that canappropriately cool a motor even in a high-temperature operationenvironment.

To solve the above problems, the present invention includes: a firstrotating shaft; a first compressor attached to the first rotating shaft,and adapted to compress an ambient gas to emit a high-pressurecompressed gas; a first motor attached to an upstream side of the firstcompressor on the first rotating shaft, and adapted to drive thecompressor; and expansion means provided at an upstream side of thecompressor, and adapted to expand a part of the ambient gas to generatea low-temperature gas to be used to cool the first motor.

Advantageous Effects of Invention

According to the present invention, a motor of a compression apparatuscan be appropriately cooled even in a high-temperature operationenvironment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a gas well in which a compressionapparatus according to a first embodiment of the present invention isinstalled.

FIG. 2 is a structural view of the compression apparatus according tothe first embodiment of the present invention.

FIG. 3 is a TS diagram illustrating a state transition of a gas used forcooling of a motor of the compression apparatus according to the firstembodiment of the present invention.

FIG. 4 is a structural view of a compression apparatus according to asecond embodiment of the present invention.

FIG. 5 is a structural view of a compression apparatus according to athird embodiment of the present invention.

FIG. 6 is a structural view of a compression apparatus according to afourth embodiment of the present invention.

FIG. 7 is a structural view of a compression apparatus according to afifth embodiment of the present invention.

FIG. 8 is a structural view of a compression apparatus according to asixth embodiment of the present invention.

FIG. 9 is a structural view of a compression apparatus according to aseventh embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments for implementing the present invention will bedescribed with reference to the drawings. Note that the same orequivalent portions are denoted with the same reference sign in thedrawings, and overlapping description is appropriately omitted.

First Embodiment

FIG. 1 is a sectional view of a gas well in which a compressionapparatus according to the present embodiment is installed. A gas well 1is an excavated hole reaching a gas layer 2 from the ground, and a steelpipe 70 for protecting an inner wall is installed inside the gas well 1.A compression apparatus 10 is attached to an inner wall of the steelpipe 70 at a bottom portion of the gas well 1 with a support member (notillustrated). The compression apparatus 10 is connected with a powersupply device 9 installed on the ground through a power transmissioncable 8 provided in the steel pipe 70. A packer 71 is attached in a gapbetween the compression apparatus 10 and the inner wall of the steelpipe 70. The packer 71 separates a lower side (upstream side) and anupper side (downstream side) of the compression apparatus 10 andprevents a backflow of the gas from the downstream side to the upstreamside of the compression apparatus 10. The compression apparatus 10 sucksnatural gases (hereinafter, referred to as ambient gases) 80 and 82 inthe gas layer 2 where the pressure is decreased to a level where theartesian flow is not possible, compresses the gas to an artesianpressure, and then emits the natural gas toward the ground. A compressedgas 83 emitted from the compression apparatus 10 rises in the steel pipe70 and flows in an artesian manner to the ground, is sent to a separator5 through a gas transport pipe 4, and is separated to a gas componentand an oil component.

During the operation of the compression apparatus 10, about 10 to 20% ofthe power supplied to the compression apparatus 10 is converted intoheat as a power loss of a motor 40 (see FIG. 2). Therefore, thecompression apparatus 10 needs to appropriately remove the heatgenerated by the motor 40 and maintain the temperature of the motor 40to be a predetermined temperature or less, in order to securereliability of an insulating material of a coil (not illustrated) builtin the motor 40, and in order to prevent demagnetization of a permanentmagnet (not illustrated) built in the motor 40.

FIG. 2 is a structural view of the compression apparatus according tothe present embodiment. The compression apparatus 10 includes a casing11 that forms an outline of the compression apparatus, a rotating shaft50 rotatably supported to an inner center of the casing 11 with bearings60 and 61, and a main compressor 30, a sub compressor 31, the motor 40,and a turbine 20, which are attached in order from the downstream sideof the rotating shaft 51. The casing 11 has different inner diameters ina portion that houses the main compressor 30 having a large outerdiameter, and a portion that houses the turbine 20, the motor 40, andthe sub compressor 31 having a small outer diameter. A step surface 11 ais formed at the upstream side of the main compressor 30. A dischargeport 14 through which the compressed gas 83 discharged from the maincompressor 30 is emitted is formed in an upper end surface of the casing11. A plurality of main suction ports 12 leading to a vicinity of aninlet of the main compressor 30 is formed in the step surface 11 a ofthe casing 11. A sub suction port 13 leading to a vicinity of an inletof the turbine 20 is formed in a lower end surface of the casing 11.

The ambient gas 80 sucked through the sub suction port 13 passes throughthe turbine 20 and is adiabatically expanded to become a low-pressurelow-temperature gas (hereinafter, referred to as low-temperature gas)81. The low-temperature gas 81 cools the motor 40 while passing aroundthe motor. The low-temperature gas 81 used to cool the motor 40 iscompressed to a pressure nearly equal to the ambient gas 82 in the subcompressor 31. The gas compressed in the sub compressor 31 is mixed withthe ambient gas 82 sucked through the main suction port 12 andcompressed to a predetermined pressure in the main compressor 30 tobecome the compressed gas 83, and is emitted toward the ground.

FIG. 3 is a TS diagram illustrating a state transition of the gas thatcools the motor 40 of the compression apparatus 10. While an existingturbine or compressor cannot realize an isentropic process, processes ofthe turbine and the compressor are expressed in the isentropic processin FIG. 3, for simplification of the description and easy understandingof the operation. In FIG. 3, a point 111 indicates a state of theambient gas 80 sucked through the sub suction port 13. The ambient gas80 in the state of the point 111 is adiabatically expanded in theturbine 20 and is decreased in the temperature and the pressure, therebyto become the low-temperature gas 81, and reaches a state indicated by apoint 112. The low-temperature gas 81 absorbs the heat of the motor 40at constant pressure, thereby to be increased in the temperature, andreaches a state indicated by a point 113. The low-temperature gas 81used to cool the motor 40 is adiabatically compressed in the subcompressor 31, thereby to be increased in the temperature, and reaches astate of a point 114. Next, the low-temperature gas 81 is mixed with theambient gas 82 sucked through the main suction port 12, thereby to bedecreased in the temperature, and reaches a state of a point 115.Finally, the gas is adiabatically compressed in the main compressor 30,and is increased in the temperature and the pressure, thereby to becomethe compressed gas 83, and is emitted to an outside through thedischarge port 14 in a state illustrated by a point 116. As describedabove, the thermal energy absorbed from the motor 40 is transported tothe ground while being maintained as the internal energy of the gaswithout being leaked to an outside with a radiator and the like.Therefore, the state transition of the gas used to cool the motor 40does not form a closed cooling cycle.

According to the present embodiment configured as described above, theambient gas 80 sucked through the sub suction port 13 is adiabaticallyexpanded in the turbine 20 and converted into the low-temperature gas81, and the low-temperature gas 81 is brought to circulate around themotor 40, so that the motor 40 can be maintained to a lower temperaturethan an ambient environment. As a result, reliability of the insulatingmaterial of the motor 40 can be secured, or a cheaper insulatingmaterial can be used. Further, the heat absorbed from the motor 40 isdischarged as internal energy of the compressed gas 83, so that it isnot necessary to provide a radiating fin and the like for cooling themotor 40 on an outside surface of the casing 11, and downsizing of thecompression apparatus 10 becomes possible.

Note that, in the compression apparatus 10 according to the presentembodiment, the motor 40 drives the sub compressor 31, in addition tothe main compressor 30. Therefore, the power consumption of the motor 40is increased, compared with a configuration of driving the maincompressor 30 only. However, the energy collected in the turbine 20 whenthe ambient gas 80 is adiabatically expanded is used to drive the subcompressor 31, so that the power necessary to drive the sub compressor31 can be suppressed.

Further, a heat loss of the motor 40 is about 10 to 20% of suppliedpower. Therefore, the amount of gas necessary to remove the heat doesnot need the total amount of the ambient gases 80 and 82 sucked by thecompression apparatus 10. In the compression apparatus 10 in the presentembodiment, only a part of the ambient gases 80 and 82 (the ambient gas80 sucked through the sub suction port 13) is adiabatically expanded andis used for cooling. Therefore, the capacity of the turbine 20 and thesub compressor 31 can be suppressed to about the several part of themain compressor 30, compared with the case where the total amount isexpanded, and the power necessary to generate the low-temperature gas 81can be suppressed.

Further, the low-temperature gas 81 used for cooling is compressed to apressure nearly equal to the ambient gas 82 in the sub compressor 31, sothat the pressure near the inlet of the main compressor 30 can bemaintained constant, and a decrease in compression efficiency due to themain compressor 30 can be prevented.

Second Embodiment

FIG. 4 is a structural view of a compression apparatus according to asecond embodiment of the present invention. Hereinafter, differentpoints of a compression apparatus 10A according to the presentembodiment from the compression apparatus 10 (see FIG. 2) according tothe first embodiment will be mainly described.

A sub compressor 31 of the compression apparatus 10A according to thepresent embodiment is attached to a hollow rotating shaft 52 at animmediate downstream position of a motor 40, the rotating shaft 52 beingrotatably supported around a rotating shaft 50 with bearings 64 and 65.A motor 42 is attached at an immediate upstream position of the subcompressor 31 on the rotating shaft 52. Meanwhile, a turbine 20 isattached to a hollow rotating shaft 51 at an immediate upstream positionof the motor 40, the rotating shaft 51 being rotatably supported aroundthe rotating shaft 50 with bearings 62 and 63. A generator 41 isattached at an immediate downstream position of the turbine 20 on therotating shaft 51.

The sub compressor 31 is driven by the motor 42, and the generator 41 isdriven by power collected in the turbine 20. The power generated in thegenerator 41 is supplied to the motor 42, as needed, and is used todrive the sub compressor 31.

The present embodiment configured as described above can also achievesimilar effects to the first embodiment. Further, the turbine 20, thesub compressor 31, and a main compressor are rotated in anon-synchronized manner, whereby the compression apparatus 10A canflexibly support change of an environmental condition such as thepressure of an ambient gas 80 or the pressure of a compressed gas 83,and a wide range of operation conditions including a condition of at thetime of startup.

Third Embodiment

FIG. 5 is a structural view of a compression apparatus according to athird embodiment of the present invention. Hereinafter, different pointsof a compression apparatus 10B according to the present embodiment fromthe compression apparatus 10 (see FIG. 2) according to the firstembodiment will be mainly described.

A power transmission cable 8 of the compression apparatus 10B accordingto the present embodiment passes through a cable protection pipe 94 andis arranged in a steel pipe 70. The cable protection pipe 94 isconfigured from a heat insulating member, and prevents intrusion of heatfrom a high-temperature compressed gas 83 into the cable protection pipe94. A heat exchanger 90 is provided near an inner wall of the steel pipe70 and outside a casing 11. One end of one passage 90 a of the heatexchanger 90 communicates into a vicinity of an outlet of a turbine 20in the casing 11 through a gas transport pipe 91, and the other end ofthe passage 90 a communicates into a vicinity of an inlet of a subcompressor 31 in the casing 11 through a gas transport pipe 92. One endof the other passage 90 b of the heat exchanger 90 communicates into avicinity of an outlet of a main compressor 30 in the casing 11 through agas transport pipe 93, and the other end of the passage 90 bcommunicates into the cable protection pipe 94.

A part of a low-temperature gas 81 is guided from the vicinity of theoutlet of the turbine 20 to the heat exchanger 90 through the gastransport pipe 91, exchanges heat with apart of the compressed gas 83guided through the gas transport pipe 93, is then guided to the vicinityof the inlet of the sub compressor 31 through the gas transport pipe 92,and is joined with the low-temperature gas 81 used to cool a motor 40.Meanwhile, a part of the compressed gas 83 guided through the gastransport pipe 93 becomes a low-temperature compressed gas (hereinafter,referred to as low-temperature compressed gas) 84 by heat exchange witha part of the low-temperature gas 81 guided through the gas transportpipe 91, and flows into the cable protection pipe 94. A low-temperaturecompressed gas 84 rises in the cable protection pipe 94 while coolingthe power transmission cable 8, and is joined with the compressed gas 83on the ground. Here, a configuration to cause a part of thelow-temperature gas 81 to flow into the cable protection pipe can beconsidered. However, the pressure of the low-temperature gas 81 is lessthan an artesian pressure, and the low-temperature gas 81 flowing intothe cable protection pipe 94 cannot reach the ground. Therefore, theconfiguration to cause a part of the low-temperature gas 81 to flow intothe cable protection pipe 94 is difficult to cool the entire powertransmission cable 8.

The present embodiment configured as described above can also achievesimilar effects to the first embodiment. Further, the power transmissioncable 8 is arranged in the cable protection pipe 94 having a heatinsulation property, and a part of the compressed gas 83 is convertedinto the low-temperature compressed gas 84 by the heat exchange with apart of the low-temperature gas 81, and is sent to the ground throughthe cable protection pipe 94, whereby the power transmission cable 8 canbe protected from the heat of the compressed gas 83.

Fourth Embodiment

FIG. 6 is a structural view of a compression apparatus according to afourth embodiment of the present invention. Hereinafter, differentpoints of a compression apparatus 10C according to the presentembodiment from the compression apparatus 10 (see FIG. 2) according tothe first embodiment will be mainly described.

A motor 40 of the compression apparatus 10C according to the presentembodiment is attached at an immediate upstream position of a turbine 20on a rotating shaft 50, and a sub suction port 13 is formed near aninlet of the turbine 20 in a side surface of a casing 11. One end of aheat transport pipe 100 is wound around an outer periphery of the motor40, and the other end of the heat transport pipe 100 is connected to aradiator 101 arranged between the turbine 20 and a sub compressor 31.Heat generated in the motor 40 is transported to the radiator 101through the heat transport pipe 100, and is emitted into alow-temperature gas 81 by the radiator 101. As the heat transport pipe,a device such as a heat pipe or a thermosiphon, to which phase change ofa coolant is applied, is favorable.

The present embodiment configured as described above can also achievesimilar effects to the first embodiment. Further, the motor 40 isarranged at an upstream side of the turbine 20 further separated from amain compressor 30 that becomes a high temperature, instead of at adownstream side of the turbine 20, whereby an increase in thetemperature of the motor 40 can be suppressed.

Fifth Embodiment

FIG. 7 is a structural view of a compression apparatus according to afifth embodiment of the present invention. Hereinafter, different pointsof a compression apparatus 10D according to the present embodiment fromthe compression apparatus 10 (see FIG. 2) according to the firstembodiment will be mainly described.

A motor 40 of the compression apparatus 10D according to the presentembodiment is attached at an immediate upstream position of a maincompressor 30 on a rotating shaft 50, and a turbine 20 and a subcompressor 31 are attached to a hollow rotating shaft 51 at an immediateupstream position of the motor 40, the rotating shaft 51 being rotatablysupported around a rotating shaft 50 with bearings 62 and 63. A motor 42is attached at an immediate downstream position of the sub compressor 31on the rotating shaft 51. The turbine 20 and the sub compressor 31 arepartitioned to the upstream side and to the downstream side with apartition 15. A gas transport pipe 95 is attached to outer peripheralportions of the motors 40 and 42, and both ends of the gas transportpipe 95 are open to a vicinity of an outlet of the turbine 20 at theupstream side of the partition 15, and to a vicinity of an inlet of thesub compressor 31 at the downstream side of the partition 15.

The turbine 20 and the sub compressor 31 are driven by the motor 42. Alow-temperature gas 81 discharged from the turbine 20 flows into the gastransport pipe 95 and is used to cool the motors 40 and 42, and is thenguided to the vicinity of the inlet of the sub compressor 31.

The present embodiment configured as described above can also achievesimilar effects to the first embodiment. Further, the turbine 20 and thesub compressor 31 are rotated in non-synchronization with the maincompressor 30, whereby the compression apparatus 10D can support a widerange of operation conditions. Note that the motor 40 and the motor 42may be installed at an upstream side of the turbine 20. In that case, aheat transport pipe 100 (see FIG. 6) to which the phase change of acoolant is applied, which has been described in the fourth embodiment,can be used in place of the gas transport pipe 95.

Sixth Embodiment

FIG. 8 is a structural view of a compression apparatus according to asixth embodiment of the present invention. Hereinafter, different pointsof a compression apparatus 10E according to the present embodiment fromthe compression apparatus 10 (see FIG. 2) according to the firstembodiment will be mainly described.

The compression apparatus 10E according to the present embodimentincludes an expansion valve 21 in place of a turbine 20 (see FIG. 2). Anambient gas 80 sucked through a sub suction port 13 passes through theexpansion valve 21 and is adiabatically expanded, thereby to become alow-temperature gas 81.

The present embodiment configured as described above can also obtainsimilar effects to the first embodiment. Further, the turbine is notincluded. Therefore, the structure of the compression apparatus 10E issimplified.

Seventh Embodiment

FIG. 9 is a structural view of a compression apparatus according to aseventh embodiment of the present invention. Hereinafter, differentpoints of a compression apparatus 10F according to the presentembodiment from the compression apparatus 10 (see FIG. 2) according tothe first embodiment will be mainly described.

The compression apparatus 10F according to the present embodiment doesnot include a sub compressor 31 (see FIG. 2), and a turbine 20 isattached to a rotating shaft 53 at an upstream side of a rotating shaft50, the rotating shaft 53 being supported with bearings 64 and 65independently of the rotating shaft 50. A generator 41 is attached at animmediate downstream position of the turbine 20 on the rotating shaft53. The generator 41 is connected through a cable 120 to a heater 121arranged outside a casing 11.

When a main compressor 30 is driven by a motor 40, the downstream sideof the turbine 20 becomes low pressure, and an ambient gas 80 suckedthrough a sub suction port 13 passes through the turbine 20 and isadiabatically expanded, thereby to become a low-temperature gas 81. Thelow-temperature gas 81 cools the motor 40 while passing around the motor40. The low-temperature gas 81 used to cool the motor 40 is mixed withan ambient gas 82 sucked through a main suction port 12, and compressedin the main compressor 30 to become a compressed gas 83, and is emittedthrough a discharge port 14. Energy collected in the turbine 20 isconverted into power by the generator 41, and is further converted intoheat in the heater 121. The heat generated in the heater 121 is radiatedinto the compressed gas 83, and is sent to the ground together with thecompressed gas 83.

The present embodiment configured as described above can also obtainsimilar effects to the first embodiment. Further, the sub compressor isnot included. Therefore, the structure of the compression apparatus 10Fis simplified. Further, the turbine 20 is attached to the rotating shaft53 dependent of the rotating shaft 50. Therefore, control to bring themain compressor 30 and the turbine 20 to be in cooperation with eachother becomes unnecessary at the time of startup. Therefore, the controlof the compression apparatus 10 can be simplified. Note that, in FIG. 9,the heater 121 is arranged at the downstream side of the compressionapparatus 10. However, the heater 121 can be arranged at an upstreamside.

Note that the present invention is not limited to the above-describedembodiments, and includes various modifications. For example, theabove-described embodiments have been described in detail to easilydescribe the present invention, and the present invention is notnecessarily limited to one including all the described configurations.Further, a part of configurations of a certain embodiment can bereplaced with a configuration of another embodiment. Further, aconfiguration of another embodiment can be added to a configuration of acertain embodiment. Further, another configuration can be addedto/deleted from/replaced with a part of a configuration of eachembodiment.

REFERENCE SIGNS LIST

10, 10A, 10B, 10C, 10D, 10E, and 10F compression apparatus

20 turbine (expansion means)

21 Expansion valve (expansion means)

30 main compressor (first compressor)

31 sub compressor (second compressor)

40 and 42 motor

41 generator

50 rotating shaft (first rotating shaft)

51 and 53 rotating shaft (second rotating shaft)

80 and 82 ambient gas

81 low-temperature gas

83 compressed gas

84 low-temperature compressed gas

90 heat exchanger

94 cable protection pipe

100 heat transport pipe

101 radiator

1. A compression apparatus comprising: a first rotating shaft; a firstcompressor attached to the first rotating shaft, and adapted to compressan ambient gas to emit a high-pressure compressed gas; a first motorattached to an upstream side of the first compressor on the firstrotating shaft, and adapted to drive the compressor; and expansion meansprovided at an upstream side of the compressor, and adapted to expand apart of the ambient gas to generate a low-temperature gas to be used tocool the first motor.
 2. The compression apparatus according to claim 1,further comprising: a second compressor provided at the upstream side ofthe first compressor and at a downstream side of the expansion means,and adapted to compress the low-temperature gas used to cool the firstmotor to a pressure equal to the ambient gas, wherein the firstcompressor mixes and compresses the low-temperature gas compressed bythe second compressor, and a part of the remaining ambient gas togenerate the compressed gas.
 3. The compression apparatus according toclaim 1, wherein the expansion means is a turbine.
 4. The compressionapparatus according to claim 2, wherein the turbine is attached to thefirst rotating shaft, and is driven by the first motor.
 5. Thecompression apparatus according to claim 2, further comprising: a secondrotating shaft provided independently of the first rotating shaft; and asecond motor attached to the second rotating shaft, wherein the turbineis attached to the second rotating shaft, and driven by the secondmotor, and the expansion means expands a part of the ambient gas togenerate the low-temperature gas to be used to cool the first motor andthe second motor.
 6. The compression apparatus according to claims 1 to5 claim 1, the compression apparatus being a downhole compressionapparatus installed in a gas well, and the compression apparatus furthercomprising: a power supply device arranged on a ground; a powertransmission cable that connects the power supply device and thedownhole compression apparatus; a cable protection pipe inserted intothe power transmission cable; and a heat exchanger provided between thecable protection pipe and the downhole compression apparatus, andadapted to convert a part of the compressed gas into a low-temperaturecompressed gas by exchanging heat with a part of the low-temperaturegas, and to cause the low-temperature compressed gas to flow into thecable protection pipe.
 7. The compression apparatus according to claim1, further comprising: a radiator installed on a downstream side of theexpansion means; and a heat transport pipe that connects the first motorand the radiator.
 8. The compression apparatus according to claim 1,wherein the expansion means is an expansion valve.